1. Field of the Invention
The present invention relates to a liquid ejection apparatus used in ink jet printing apparatus and the like and also to a method of controlling the same.
2. Description of the Related Art
A general suction-based recovery operation employed in the ink jet printing apparatus will be briefly explained.
In executing the suction-based recovery operation, a general ink jet printing apparatus first causes a cap, which receives sucked-out ink, to come into contact with that face of an ink jet print head (hereinafter also referred to simply as a print head) in which nozzle ports for ink ejection are formed. Next, a suction pump connected to the cap is driven to produce a negative pressure in the cap to suck the viscous ink from the nozzle ports out into the cap. At this time, since the sucked-out ink is discarded as waste ink, the sucking of ink in an amount more than necessary is not desirable. Therefore, a general ink jet printing apparatus, after a predetermined duration of driving the suction pump, opens a release valve on the cap. Alternatively, the cap is parted from the nozzle ports to introduce an atmospheric pressure into the cap, thus limiting the amount of ink being sucked out to the minimum required.
In returning the interior of the cap to the atmospheric pressure, if an absolute value of the negative pressure in the ink jet print head is too large, the ink that has been sucked out into the cap may get back into the print head. As it is brought back into the print head, the ink may carry with it foreign matters, such as dirt in the cap, into the print head, resulting in improper ejections. In an ink jet printing apparatus constructed to suck out different colors of ink through a common cap, a so-called color mixing may result at time of ink ejection.
Japanese Patent Application Laid-Open No. 2005-144939 discloses a technique for preventing color mixing, employed in an ink jet printing apparatus that sucks out different colors of ink through a common cap. Japanese Patent Application Laid-Open No. 2005-144939 prevents the color mixing by supplying ink from an ink cartridge to subtanks to lower the absolute values of the negative pressures in the subtanks or to make the negative pressures equal for all colors.
However, experiments of the inventors have found that even if the negative pressures of the subtanks for different colors were set equal, too large an absolute value of the negative pressure in the print head when the interior of the cap is returned to an atmospheric pressure can result in the color mixing.
Generally, only supplying ink from the ink cartridge to the subtanks cannot lower the absolute values of negative pressure in the subtanks. To lower the absolute values of negative pressure in the subtanks requires, as disclosed in Japanese Patent Application Laid-Open No. 2005-144939, a negative pressure generation mechanism or the like in the subtanks, making the apparatus complicated.